Very accurate oscillatory frequencies can be constantly obtained with the piezoelectric oscillators in which piezoelectric oscillation elements, for example, crystal oscillation plates, are used. Such piezoelectric oscillators are, therefore, conventionally employed in diverse fields as reference frequency sources for electronic devices. The piezoelectric oscillators typically have a structure where an integrated circuit element is housed in a housing portion of an insulating base with an opening on its upper-surface side, a piezoelectric oscillation element is securely supported in the upper direction of the integrated circuit element, and a cover is provided to hermetically seal the interior of the base.
One can simplify the structure of such a piezoelectric oscillator with a relatively small number of components by customizing a one-chip integrated circuit element in which an inverter amplifier, for example, CMOS, is provided as an oscillation amplifier, contributing to cost reduction.
In recent years, flip-chip bonding is often employed in such piezoelectric oscillators because this bonding technique, in contrast to wire bonding, reduces the piezoelectric oscillators in size and height. As disclosed in the patent document 1, pads of an integrated circuit element are flip-chip bonded, by means of metallic bumps made of such a material as gold, to internal terminal pads in a housing portion of a ceramic base by supersonic thermocompression bonding.
FIG. 7 illustrates an example of piezoelectric oscillator circuits to be housed in the base. In the drawing, 100 is an integrated circuit element, and 200 is a piezoelectric oscillation element. The integrated circuit element 100 includes, for example, inverter amplifiers AMP1 and AMP2, a feedback resistor Rf, a limiting resistor Rd, and capacitors C1 and C2. Referring to the other reference symbols, P1 to P3 are signal input and output portions of the integrated circuit element 100, and P4 and P5 are signal input and output portions of the piezoelectric oscillation element 200. An alternating current signal or a high frequency signal i1 is outputted from the output portion P3 of the integrated circuit element 100. An alternating current signal i2 flows between the input and output portions P5 and P4 of the piezoelectric oscillation element 200 and the input and output portions P1 and P2 of the integrated circuit element 100. The integrated circuit element and the piezoelectric oscillation element are thus connected in the circuit and housed in the base. In the base, the input and output portions P1 to P5 for the signals i1 and i2 are connected by means of the pads of the integrated circuit element, internal terminal pads of the base, pads of the piezoelectric oscillation element, and wiring patterns.